With respect to a wireless communication system, as a request for a bandwidth gradually increases, it has led a study and development for a millimeter radio wave communication system. However, a very high penetration loss and a very high absorption loss have been problematic and to solve this problem, a beamforming (BF) has been required. For this BF technique, there exist an analog BF (ABF) and a digital BF (DBF).
However, a technique of a mixed analog and digital BF has not been sufficiently studied.